1. Field of the Invention
The present invention relates to an electron beam exposure apparatus and, more particularly, to an electron beam exposure apparatus for drawing a pattern on a wafer or drawing a pattern on a mask or reticle using a plurality of electron beams, and its control method.
2. Description of the Related Art
An electron beam exposure apparatus includes a point beam type apparatus which uses a beam shaped in a spot pattern, a variable rectangular beam type apparatus which uses a beam shaped to have a rectangular section with a variable size, a stencil mask type apparatus which shapes a beam into a desired sectional shape using a stencil, and the like.
The point beam type electron beam exposure apparatus is used for only research purposes due to its low throughput. The variable rectangular beam type electron beam exposure apparatus has a throughput higher by one or two orders of magnitude than that of the point beam type, but suffers problems in terms of throughput when highly integrated patterns having a line width as small as about 0.1 .mu.m are to be formed by exposure. On the other hand, the stencil mask type electron beam exposure apparatus uses a stencil mask formed with a plurality of repetitive pattern through holes in a portion corresponding to a variable rectangular aperture. Hence, the stencil mask type electron beam exposure apparatus is effective for exposure of repetitive patterns. However, when a semiconductor circuit requires a large number of transfer patterns that cannot be formed on a single stencil mask, a plurality of stencil masks must be prepared in advance, and must be used one by one, resulting in a long mask exchange time and a considerable throughput drop.
As an apparatus that can solve the above problems, a multi-electron beam type exposure apparatus is known. In this apparatus, a plurality of electron beams are irradiated on the sample surface along the course of design coordinate positions, and are deflected along that course of design coordinate positions to scan the sample surface. In addition, the plurality of electron beams are individually ON/OFF-controlled in correspondence with the pattern to be drawn, thereby drawing the pattern. Since the multi-electron beam type exposure apparatus can draw an arbitrary pattern, it can improve the throughput.
FIG. 15A schematically shows the multi-electron beam type exposure apparatus. Reference numerals 501a, 501b, and 501c denote electron guns that can individually ON/OFF-control electron beams. Reference numeral 502 denotes a reduction electron optical system for projecting a plurality of electron beams emitted by the electron guns 501a, 501b, and 501c onto a wafer 503 in a reduced scale; and 504, a deflector for deflecting the plurality of electron beams to be projected onto the wafer 503 in the reduced scale.
The plurality of electron beams coming from the electron guns 501a, 501b, and 501c are deflected by an identical amount by the deflector 504. With this deflection, the respective electron beams are deflected while sequentially settling their positions on the wafer in accordance with a matrix having a matrix spacing defined by the minimum deflection width of the deflector 504 with reference to their beam reference positions. The individual electron beams form exposure patterns on different exposure regions by exposure.
FIGS. 15B to 15D show the state wherein the electron beams coming from the electron guns 501a, 501b, and 501c expose the corresponding exposure regions to form exposure patterns in accordance with an identical matrix. The respective electron beams move while settling their positions on the matrix at the same time like (1, 1), (1, 2), . . . , (1, 16), (2, 1), (2, 2), . . . , (2, 16), (3, 1), . . . , and expose the corresponding regions to form patterns (P1, P2, P3) by turning on the beams at the positions of the exposure patterns (P1, P2, P3).
In the multi-electron beam type exposure apparatus, since the respective beams simultaneously form different patterns, the size of each electron beam and the minimum deflection width of the deflector 504 corresponding to that size are set in correspondence with the minimum line width of the exposure patterns. As the minimum line width becomes smaller, the number of times of exposure while settling the electron beam positions increases, resulting in a considerable throughput drop.
The exposure patterns do not always equally include patterns with a minimum line width. However, conventionally, even in a region defined by a pattern having a line width larger than the minimum line width, exposure is done using the electron beam size and the minimum deflection width corresponding to that size, determined based on the minimum line width in all the patterns. For this reason, the throughput drops as the minimum line width of the pattern shrinks.